From d3728fb71278e411749664172c92dbfb157bbf09 Mon Sep 17 00:00:00 2001
From: Aster Seker <git.electroyar@gmail.com>
Date: Fri, 5 Sep 2025 23:37:27 +0300
Subject: [PATCH] feat(pbkdf2): enforce iteration limit

Add configurable MAX_PBKDF2_ITERATIONS and reject too-high iteration counts. Test limit boundaries.
---
 include/hmac_cpp/hmac_utils.hpp |  6 ++++++
 src/hmac_utils.cpp              |  5 ++++-
 test_all.cpp                    | 15 +++++++++++++++
 3 files changed, 25 insertions(+), 1 deletion(-)

diff --git a/include/hmac_cpp/hmac_utils.hpp b/include/hmac_cpp/hmac_utils.hpp
index 1539904..87a64ed 100644
--- a/include/hmac_cpp/hmac_utils.hpp
+++ b/include/hmac_cpp/hmac_utils.hpp
@@ -6,8 +6,14 @@
 #include <string>
 #include <vector>
 
+#ifndef HMAC_CPP_MAX_PBKDF2_ITERATIONS
+#define HMAC_CPP_MAX_PBKDF2_ITERATIONS 1000000u
+#endif
+
 namespace hmac_cpp {
 
+    static constexpr uint32_t MAX_PBKDF2_ITERATIONS = HMAC_CPP_MAX_PBKDF2_ITERATIONS;
+
     /// \brief Compares two byte arrays in constant time
     /// \param a Pointer to first array
     /// \param a_len Length of the first array
diff --git a/src/hmac_utils.cpp b/src/hmac_utils.cpp
index b864e0a..23acc7d 100644
--- a/src/hmac_utils.cpp
+++ b/src/hmac_utils.cpp
@@ -40,6 +40,8 @@ namespace hmac_cpp {
             throw std::invalid_argument("Null pointer with non-zero length");
         if (iterations < 1)
             throw std::invalid_argument("PBKDF2: iterations must be >= 1");
+        if (iterations > MAX_PBKDF2_ITERATIONS)
+            throw std::invalid_argument("PBKDF2: iterations too large");
         if (dk_len == 0)
             throw std::invalid_argument("PBKDF2: dk_len must be positive");
         if (salt_len < 16)
@@ -115,7 +117,8 @@ namespace hmac_cpp {
             (salt_len > 0 && salt_ptr == nullptr) ||
             out_ptr == nullptr)
             return false;
-        if (iterations < 1 || dk_len == 0 || salt_len < 16)
+        if (iterations < 1 || dk_len == 0 || salt_len < 16 ||
+            iterations > MAX_PBKDF2_ITERATIONS)
             return false;
 
         const size_t hlen = hmac_hash::SHA256::DIGEST_SIZE;
diff --git a/test_all.cpp b/test_all.cpp
index 1da1be3..b604b00 100644
--- a/test_all.cpp
+++ b/test_all.cpp
@@ -237,6 +237,13 @@ TEST(PBKDF2Validation, TooLargeDkLenThrows) {
     EXPECT_THROW(hmac::pbkdf2("password", salt, 1, too_large, hmac::Pbkdf2Hash::Sha1), std::invalid_argument);
 }
 
+TEST(PBKDF2Validation, IterationsLimit) {
+    std::string salt(16, 'a');
+    uint32_t limit = hmac::MAX_PBKDF2_ITERATIONS;
+    EXPECT_NO_THROW(hmac::pbkdf2("password", salt, limit - 1, 32, hmac::Pbkdf2Hash::Sha256));
+    EXPECT_THROW(hmac::pbkdf2("password", salt, limit + 1, 32, hmac::Pbkdf2Hash::Sha256), std::invalid_argument);
+}
+
 TEST(PBKDF2Test, SHA256WithValidSalt) {
     auto salt = from_hex("000102030405060708090a0b0c0d0e0f");
     std::string salt_str(salt.begin(), salt.end());
@@ -256,6 +263,14 @@ TEST(PBKDF2BufferApiTest, SHA256ArrayOutput) {
     EXPECT_TRUE(std::equal(out.begin(), out.end(), ref.begin()));
 }
 
+TEST(PBKDF2BufferApiTest, IterationsLimit) {
+    std::string salt(16, 'a');
+    std::array<uint8_t,32> out{};
+    uint32_t limit = hmac::MAX_PBKDF2_ITERATIONS;
+    EXPECT_TRUE(hmac::pbkdf2_hmac_sha256(std::string("password"), salt, limit - 1, out));
+    EXPECT_FALSE(hmac::pbkdf2_hmac_sha256(std::string("password"), salt, limit + 1, out));
+}
+
 // SHA512 vector from BoringSSL pbkdf_test.cc
 TEST(PBKDF2Test, BoringSSL_SHA512) {
     auto dk = hmac::pbkdf2("passwordPASSWORDpassword",